Boyfriend thinks he's cheating on his children with me?

In his marriage my boyfriend and his wife had no emotional or physical connection for many years. The kisses and the snuggles all came from his children. His children are teenagers wanting to grow up, and this makes my boyfriend sad. Also, he informed me that now that his adult conversations and affections come from me, he feels as though he’s “cheating” on his children. He is not unaffectionate with his kids, but they are growing up and away not wanting to be kissed or conversant. Is this feeling of obtaining the appropriate love and discussion with me as “cheating” something that he can get over. He admits that his kids did occupy an unhealthy role in his life of being literally everything as he had no relationship with their mother. Have any of you struggled with this or have any ideas how to handle this situation?